Search entire multi level cell array for matching string

I am trying to search a cell of cell arrays for a matching string without using a for loop due to the inefficiency and speed. My first idea was to use an anonymous function and strip out the top layer iteratively of the cell array in the form of

 cellfun(@(cell) cell{1}, MyCellofCellArray, 'UniformOutput', false);

However, let's say for example I have an uneven cell of cell array where

 MyCellArray{1} = 1x1 cell, 
 MyCellArray{2} = 1x2 cell,
 MyCellArray{3} = 1x3 cell.

If you try to use the aforementioned cellfun, you get an error "Index exceeds matrix dimensions" because MyCellArray{1} only contains a 1x1 cell. Anyone have any ideas or suggestions?

Thanks,

JWelch

[Cedric]

Could you provide an example, and indicate what you are looking for? I.e. do you need to extract chunks of matched strings, IDs of external and internal cell arrays, ..?

[Josh Welch]

I just need to extract the index of the array element of the matching string. Each element of the array contains just one string.

i.e. MyCellArray{1} = {'str11'}, MyCellArray{2} = {'str21','str22'}, MyCellArray{3} = {'str31','str32','str33'}. I would like to find the indices of cell 'str32' in MyCellArray. The element is accessed via MyCellArray{3}{2} so 3, 2 would be the answer.

[Cedric]

Which version of MATLAB do you have? Also, are you search for unique keywords, for the first when there are multiple, or for all occurrences?

Answer 1

[James Tursa]

Does this do what you want?

mystring = whatever string you are trying to find
MyCellArrays = [cellfun(@(x)x(:)',MyCellArray,'UniformOutput',false)];
NewCellArrays = [MyCellArrays{:}];
x = find(~cellfun(@isempty,strfind(NewCellArrays,mystring)));
n = cellfun(@numel,MyCellArray);
nsum = cumsum(n);
first = find(nsum>=x,1);
if( first == 1 )
    second = x;
else
    second = x - nsum(first-1);
end

The element is then MyCellArray{first}{second}

If the string is not guaranteed to be present, then test for x being empty before executing the remaining code.

[Josh Welch]

This code actually will work. I was hoping to get the indices from the original matrix but I can massage the rest of my code the same way to get the corresponding data with the same indices.

Thanks for your help!

Answer 2

[Cedric]

If you have 2015a or above, this can be an occasion for playing with the new REPELEM function:

 linId  = strcmpi( [MyCellArray{:}], 'str32' ) ;
 lookup = repelem( 1:numel(MyCellArray), cellfun( @numel, MyCellArray )) ;
 id     = [lookup(linId), sum( lookup(1:find(linId) == lookup(linId)) )] ;

This produces

 id =
     3     2

[Josh Welch]

I tried this code which is extremeley elegant, but I don't have 2015. When I upgrade, REPELEM is definitely going in my bag of tricks... thanks for your input

[Cedric]

My pleasure! I discovered REPELEM last week actually, so I'm glad to have had this occasion for playing a bit with it. Just for those who don't have 2015a or above, here is the output of intermediary steps:

 linId =
     0     0     0     0     1     0

 lookup =
     1     2     2     3     3     3